1. Field of the Invention
This invention relates to the removal of uranium-based contaminants from groundwater.
2. Description of Related Art
Groundwater in many localities has become contaminated by both natural and manmade impurities. Due to the considerable reliance on groundwater as a primary source of potable water, treatment of polluted groundwater to remove such contaminants has gained significant interest within the last decade. Many treatment systems for the removal of groundwater contaminants have been proposed, including pump-and-treat systems, well injection of treatment agents, and in-situ treatment. Due to the significant cost savings, in-situ treatment of groundwater has drawn considerable interest in recent years. In-situ treatment of groundwater is discussed in NEW APPROACH TO IN-SITU TREATMENT OF CONTAMINATED GROUNDWATER: McMurty et at., Environmental Progress 1985.
McMurty discusses the use of permeable barrier walls placed in trenches excavated into native aquifers to treat contaminated groundwater. The permeable barrier contains appropriate treatment media, such that the quality of the contaminated groundwater flowing through the media is significantly improved. McMurtry states that most in-situ groundwater treatments will be in isothermal, anaerobic, reducing environments. Many in-situ groundwater treatment systems take advantage of the naturally occurring condition, in conjunction with the selected treatment material to remove or transform the chemical contaminants in the groundwater into nonhazardous material. Typically treatment materials are limestone, activated carbon, active metals, or biological agents. Alternatively, a modified in-situ treatment system maybe used, wherein tanks or chambers, which are filled with a treatment media, are buried or partially buried in the ground. Groundwater is directed to the tank by piping. The modified in-situ system maybe preferred when the natural groundwater flow is complex and multidemensional. The modified in-situ provides ease of installation in these situations. Also, ex-situ or above ground treatment systems may be used in order to reduce installation costs.
These groundwater treatment systems rely on certain process condition,to achieve the removal or adsorption of the desired contaminant. For example, the removal efficiency of the treatment material may rely on the assumption that certain constituents are present in the groundwater for treatment system to work. Alternatively, the treatment media may work more efficiently in an acidic or basic environment. Therefore, it may be necessary to pretreat or precondition the groundwater to optimize the removal or neutralization capability of the treatment media.
An object of this invention is to provide a method to optimize the treatment efficiency of the media in an ex-situ groundwater treatment system.
This and other objectives of the invention, which will become apparent from the following description, have been achieved by a novel improvement to the in-situ groundwater treatment process for removing uranium-based contaminants from contaminated groundwater comprising: Ascertain the direction, volume, rate, and chemical composition of a zone of contaminants dissolved in the groundwater flowing through an aquifer. Then select an appropriate primary treatment media that will render the contaminated material inactive within the groundwater. Next, determine the preferred chemical composition of the groundwater for treatment by the primary treatment media. A pretreatment media is provided, such that the pretreatment media adjusts the chemical composition of the contaminated groundwater to the preferred chemical composition. A first repository is provided, and the pretreatment media is placed therein. The first repository is placed such that the flow of contaminated groundwater through the first repository enters the repository through the upstream side thereof. Further the placement is such that the flow of the contaminated groundwater in the aquifer is directed to pass through the pretreatment media and exit from the downstream side thereof. The permeability of the pretreatment media being such that the resistance to the passage of groundwater through the first repository is no greater that the resistance of the native aquifer to the passage of groundwater through the aquifer. The primary treatment media is provided and placed in a second repository. The second repository is such that the flow of contaminated groundwater from the first repository enters the second repository through the upstream side thereof. Further, the placement being such that the flow of the contaminated groundwater in the aquifer is directed to pass through the pretreatment media, and exit from the downstream side thereof. The permeability of the primary media being such that the resistance to the passage of groundwater through the first repository is no greater that the resistance of the native aquifer to the passage of groundwater through the aquifer. In order to provide improved treatment of the contaminated groundwater the groundwater exiting the first repository enters a settling pond where insoluble material is permitted to settle out of the groundwater in a settling pond or the like prior to the contaminated groundwater entering the secondary repository.
For treatment of uranium-based contaminants the primary treatment elemental iron. When the uranium-based contaminated groundwater is acidic, it is preferable to increase the pH of the groundwater with an alkaline material such as limestone. Preferably the limestone contains at least 90 weight percent calcium carbonate. The groundwater maybe maintained in its native anaerobic condition or allowed to react with oxygen in the air as required.